1. Field of the Invention
The present invention relates to a method for calibrating an acceleration sensor.
2. Description of Related Art
Acceleration sensors are known in which the acceleration force acting on an inertial body is detected and measured. An insert body is maintained in a position of rest by an elastic organ, while the acceleration force acting thereupon tends to dislocate the inert body from its position of rest. As a rule, this principle does not suffice for precise measurements of accelerations associated with low frequency oscillations or even constant accelerations. In navigation technics, in particular in astronautics, there occurs the problem of determining very low acceleration values exactly and as absolute values. One difficulty presented is that the measured values of a calibrated acceleration sensor are valid only for a limited period of time, since the individual components of the measuring equipment tend to drift from fixed settings over an extended period of time. Generally, the elastic force constant of the elastic organ is known, so that the slope of the straight line representing the ratio between the magnitude of the measuring signal and of the prevailing acceleration is known. However, the origin of the respective coordinate system is unknown. It would be feasible for the calibration of an acceleration sensor to know the absolute value of acceleration obtained from a pair of values formed by the measured acceleration and the indicated acceleration. Knowing the absolute value, however, requires a calibrated second acceleration sensor.
The present inventor's copending U.S. patent application Ser. No. 420,554 describes an acceleration sensor that is calibrated by a controlled change of the mass of the inertial body by adding or absorbing a foreign substance. A first measurement is performed with a first mass value of the inertial body and a second measurement is performed with a second mass value. The difference between the mass values corresponds to a difference between the excursions of the inertial body. In this way, the absolute value of acceleration can be determined by two measurement. The acceleration sensor is calibrated by measuring the excursion at two different masses. The change of the mass of the inertial body requires a relatively great effort or particular materials that are capable of adsorbing or absorbing foreign substances.
It is an object of the present invention to provide a calibration method that does not impose any particular requirements to the shape or the constitution of the inertial body.